A problem which arises generally in relation to sprayers concerns effective penetration of the crop or other material to be sprayed, by the spray of droplets produced by the sprayer. Conventionally, various forms of spray nozzle are utilised in which a spray of droplets is produced solely by virtue of the energy derived from the supply of liquid under pressure.
However, such conventional arrangements do not achieve the level of crop penetration which can be desired.
Various attempts have been made to improve crop penetration including the use of air flow producing means in association with conventional spray nozzles. However, such an arrangement has been found to be bulky and relatively ineffective.
Attempts have also been made to utilise the effect of electrostatic charges to cause the sprayed droplets to be attracted to the crop material and deposited thereon. These also have been found to be relatively ineffective and have not been widely used.
The use of droplegs to permit crops to be sprayed from a low location generally below the canopy of leaves in the case of crops such as potatoes has been found to improve very substantially the ability to cover the under surfaces of plants, as compared with conventional spraying arrangements in which the droplets are discharged onto the canopy of leaves from above.
A further prior proposal known to the Applicants utilises an air supply in association with a liquid supply. However, the liquid supply is directed via a restrictor onto a baffle plate where primary atomisation occurs before the liquid is mixed with the compressed air. The compressed air then forces the thus-produced droplets through a circular passage onto an inner face of a flood jet. There, secondary atomisation takes place, prior to the spray emerging in a flat fan-shaped pattern. This dual stage atomisation process leads, so it is claimed, to the production of relatively large droplets in which air bubbles are trapped and which, by virtue of their size, are less subject to unwanted spray drift. It has been established that the droplets size thus produced is notably ineffective in effecting crop coverage. In practice, what is particularly wanted is the production of a droplet size similar to that which is produced in atmospheric conditions such as a misty morning in a damp climate overnight whereby the droplets which condense on surfaces such as the external surface of a standing car are of such a size that they have little tendency to roll over the surface, and they therefore stay where they are deposited. In combination with this objective, there is the corresponding need to be able to produce such droplets travelling at a sufficiently high velocity in order to penetrate the crop sufficiently.
Further prior proposals are disclosed in GB 952,457 and GB 1,378,190 and U.S. Pat. No. 4,465,832 and U.S. Pat. No. 4,179,068. These proposals involve systems for the admixture of liquid and air for liquid entrainment and/or droplet formation. The most pertinent of these with respect to the present invention is the latter U.S. Pat. No. '068 specification (assigned to NRDC) which discloses a liquid spray device in which liquid enters a swirl chamber in a generally radially inwardly-directed manner for subsequent onward movement through the open end of the swirl chamber under the action of a gas flow delivered at that open end for subsequent discharge from a spaced opening-see FIG. 2. We have established that a system in which both the airflow and the liquid flow do not proceed via an air-and-liquid supply chamber having a closed end wall or target and one or more associated outlets in the manner of the embodiments of the present invention, cannot achieve the beneficial results of the present invention and the system of this prior disclosure operates in a significantly different manner involving generally axial droplet flow (with respect to the liquid supply direction), as compared with the generally radially or outwardly directed flow of the system of the present invention (or up to 45 degrees on each side thereof). Moreover, the system of this prior U.S. Pat. No. '068 specification operates on the effective principle of the maintenance of droplet size at differing air supply pressures, whereas described embodiments of the present invention operate in a manner such that the droplet size changes with changes in system pressure.
There are disclosed in U.S. Pat. Nos. 4,828,182 and 4,899,937 (assigned to Spraying Systems Co) spray nozzle assemblies which have been marketed for use in agricultural spraying situations. The U.S. Pat. No. '182 specification discloses a spray nozzle assembly that finds particular utility in humidification and evaporative cooling applications in which it is desirable that a spray be discharged in a wide and relatively flat spray pattern, which is there contrasted with many prior air assisted nozzles which discharge with a relatively tight round spray pattern.
The system disclosed facilitates pre-atomization of liquids by means of an insert member which includes an elongated impingement element having a transversely extending circular hole which is struck by the pressurised liquid, to break up same. A pressurised stream of air is admitted to the device and a side surface area defines an impingement surface which deflects and breaks up the airstream and considerable turbulence for pre-atomizing the liquid stream is created, and as a result of the airstream being injected transversely into the longitudinally flowing liquid stream, there is produced a liquid flow in the downstream direction towards an outlet nozzle, in the form of finely divided pre-atomized particles. This preliminarily atomized liquid flow stream is then directed axially through a discharge orifice at the open end of the device and an external deflector flange which is transversely oriented to the line of travel of the liquid, directs same through a final discharge orifice where the pre-atomized droplets are broken into extremely fine liquid particles which are then deflected into a flat, wide spray pattern in a manner which maximises their exposure to the ambient air. A cup-shaped recess is believed to produce pressure waves or acoustic energy which assists in the liquid breakdown. The nozzle assembly has particular utility in humidification and evaporative cooling applications.
The U.S. Pat. No. '937 patent discloses the use of the same nozzle assembly in a manner in which it can be easily removed from the nozzle body to enable the nozzle to be used as an hydraulic nozzle.
Accordingly, it can be seen that these prior U.S. patents contain no disclosure whatever relevant to the concept of providing a chamber to which liquid and air supplies are provided, the liquid supply being in unatomised form, and the chamber having a wall or closed end towards which said air and liquid supplies are directed, and from which chamber the liquid and air supplies are discharged outwardly with respect to the closed end of the chamber through an outlet formed in a chamber side wall and in the form of an air flow with entrained liquid droplets.
There is disclosed in U.S. Pat. No. 5,129,583 (Bailey) an atomizer for discharging a jet of one fluid in another fluid. The atomizer comprises an atomizer head disposed generally in-line with the incoming water supply direction and the head is formed with at least one nozzle hole for discharging the jet through the head and generally forwardly and outwardly. The nozzle hole is profiled to reduce deposition on the atomizer when used for spraying into dust-laden flue gas. The nozzle profile is adapted to reduce turbulence. The general direction of water and air flow through the atomizer is actually lengthwise of the atomizer and onwards through the open atomizer head with the addition of a slightly outward component of movement resulting from the nozzle holes' slightly inclined attitude.
There is disclosed in U.S. Pat. No. 3,096,023 (Thomas) a system for distributing lubricant or oil to chains, gears and other machine parts. The system may be readily used with nearly all types of oils regardless of viscosities and changing temperature and humidity. The system provides a plurality of spaced outlets for application to the machine part which is to receive the lubricant. No data is provided regarding pressures needed to produce the requisite flows. Jet units apply a jet directly onto the bearings to be lubricated, or they may be provided with tube or hose connections to convey such jet to a bearing unit and thus the jet is as narrow as such tube or hose. In the embodiments other than those of FIGS. 4 and 7 the material flow is axial throughout the jet units whereby these themselves are incapable of operating in accordance with the principles of the present invention, while that of FIG. 4 shows a superficial resemblance to the latter but is used in a system whereby it produces narrowly-aimed jets of lubricant or coolant to be pin pointed on defined areas of the chains, gears or other machine parts. In the case where coolant is applied, the objective is to apply a concentrated jet of sufficient liquid volume to produce the requisite coolant effect. This is an inversion of the requirements of the present invention which, in a boom-type spraying machine, seeks to apply a uniform liquid coating of droplets, as disclosed herein, utilising the absolute minimum of liquid per unit area, while applying such coating uniformly to crop areas which can be measured in terms of hectares per unit time, instead of square centimetres per unit time.
Accordingly, there is a considerable need at least in relation to agricultural and horticultural boom type sprayers, for improvements in relation to droplet generation as discussed above, having regard to crop penetration, particle size, and minimisation of water carrying requirements, and an object of the present invention is to provide a method and apparatus offering improvements in relation to one or more of these matters, or generally.